In recent years, soft silicone hydrogel contact lenses, for example, Focus NIGHT & DAY® and O2OPTIX™ (CIBA VISION), and PureVision® (Bausch & Lomb), Acuvue® Advance™ and Acuvue® Oasys™ become more and more popular because of their high oxygen permeability and comfort. “Soft” contact lenses conform closely to the shape of the eye, so oxygen cannot easily circumvent the lens. Soft contact lenses must allow oxygen from the surrounding air (i.e., oxygen) to reach the cornea because the cornea does not receive oxygen from the blood supply like other tissue. If sufficient oxygen does not reach the cornea, corneal swelling occurs. Extended periods of oxygen deprivation cause the undesirable growth of blood vessels in the cornea. By having high oxygen permeability, a silicone hydrogel contact lens allows sufficient oxygen permeate through the lens to the cornea and to have minimal adverse effects on corneal health. However, a silicone hydrogel material typically has a surface or at least some areas of its surface which is hydrophobic (non-wettable). Hydrophobic surface or surface areas will up take lipids or proteins from the ocular environment and may adhere to the eye. Thus, a silicone hydrogel contact lens will generally require a surface modification.
In order to modify the surface hydrophilicity of contact lenses, contact lenses can be subject to surface treatment prior to cast-molding, for example, by incorporating wetting agents into a lens formulation for making the contact lenses as proposed in U.S. Pat. Nos. 4,045,547, 4,042,552, 5,198,477, 5,219,965, 6,367,929 and 6,822,016, 7,279,507. This type of method may be cost effective because after cast-molding of contact lenses there is no additional posterior surface treatment process required for modifying the surface hydrophilicity of the lens. However, the wetting agents are hydrophilic in nature and have very poor miscibility with some polymerizable hydrophobic components in silicone hydrogel lens formulation. One or more suitable compatibilizing agents must be used to render the wetting agents adequately (but still not completely) miscible with silicone hydrogel lens formulations. Choice for such compatibilizing agents is limited. Without compatibilizing agent, poor miscibility of a wetting agent with a silicone hydrogel lens formulation can cause the turbidity of the lens formulation and adversely affect the optical properties of resultant silicone hydrogel contact lenses.
Therefore, there exists a need for a method of making silicone hydrogel contact lenses having internal wetting agents and for a method of incorporating internal wetting agents into silicone hydrogel contact lenses.